将多个地图合并/合并为1个地图

Question

如何将dart中的2个或更多地图合并/合并到1个地图中？例如,我有类似的东西:

 var firstMap = {"1":"2"};
 var secondMap = {"1":"2"};
 var thirdMap = {"1":"2"};

我想要:

 var finalMap = {"1":"2", "1":"2", "1":"2"};

Answer 1

你可以使用对象的addAll方法Map

var firstMap = {"1":"2"};
var secondMap = {"2":"3"};

var thirdMap = {};

thirdMap.addAll(firstMap);
thirdMap.addAll(secondMap);

print(thirdMap);

要么

var thirdMap = {}..addAll(firstMap)..addAll(secondMap);

Answer 2

 var firstMap = {"1":"5"};
 var secondMap = {"1":"6"};
 var thirdMap = {"2":"7"};
 
 var finalMap = {...firstMap, ...secondMap, ...thirdMap};
 // finalMap: {"1":"6", "2":"7"};

"1"请注意，具有值的键"5"将被覆盖"6"。

Answer 3

使用Map.addAll,Iterable.reduce和级联运算符的替代语法，用于组合大量地图：

var combinedMap = mapList.reduce( (map1, map2) => map1..addAll(map2) );

实时飞镖示例 https://dartpad.dartlang.org/9cd116d07d2f45a9b890b4b1186dcc5e

Answer 4

我为可迭代的地图提出了一个“单行”解决方案：

var finalMap = Map.fromEntries(mapList.expand((map) => map.entries));

Answer 5

另一种选择是使用CombinedMapViewfrom package:collection：

new CombinedMapView([firstMap, secondMap])

它不会创建合并的地图，而是会创建一个同时包含两者Map的视图。